[llvm] [RISCV] Don't use pointer operand in MemoryLocation for RISC-V strided and indexed load/store intrinsics. (PR #79890)

[Craig Topper via llvm-commits]

https://github.com/topperc created https://github.com/llvm/llvm-project/pull/79890

It seems that even though we set the size to unknown, there is still an assumption in alias analysis somewhere that we will only access bytes *after* the pointer. Since a strided/indexed load/store can have negative indices, this is not accurate.

This was found in our downstream when the scheduler reordered a strided load with negative stride above a scalar store that aliased with it.

>From ec1874c991f84aa8932228fdba1f208da8f18c8f Mon Sep 17 00:00:00 2001
From: Craig Topper <craig.topper at sifive.com>
Date: Mon, 29 Jan 2024 11:53:22 -0800
Subject: [PATCH] [RISCV] Don't use pointer operand in MemoryLocation for
 RISC-V strided and indexed load/store intrinsics.

It seems that even though we set the size to unknown, there is still
an assumption in alias analysis somewhere that we will only access bytes
*after* the pointer. Since a strided/indexed load/store can have
negative indices, this is not accurate.

This was found in our downstream when the scheduler reordered a
strided load with negative stride above a scalar store that aliased
with it.
---
 llvm/lib/Target/RISCV/RISCVISelLowering.cpp | 24 ++++++++++++++-------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 05264f7fc42044b..40252a85879f605 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -1464,9 +1464,15 @@ bool RISCVTargetLowering::getTgtMemIntrinsic(IntrinsicInfo &Info,
   auto &DL = I.getModule()->getDataLayout();
 
   auto SetRVVLoadStoreInfo = [&](unsigned PtrOp, bool IsStore,
-                                 bool IsUnitStrided) {
+                                 bool IsUnitStrided, bool UsePtrVal = false) {
     Info.opc = IsStore ? ISD::INTRINSIC_VOID : ISD::INTRINSIC_W_CHAIN;
-    Info.ptrVal = I.getArgOperand(PtrOp);
+    // We can't use ptrVal if the intrinsic can access memory before the
+    // pointer. This means we can't use it for strided or indexed intrinsics.
+    if (UsePtrVal)
+      Info.ptrVal = I.getArgOperand(PtrOp);
+    else
+      Info.fallbackAddressSpace =
+          I.getArgOperand(PtrOp)->getType()->getPointerAddressSpace();
     Type *MemTy;
     if (IsStore) {
       // Store value is the first operand.
@@ -1526,7 +1532,7 @@ bool RISCVTargetLowering::getTgtMemIntrinsic(IntrinsicInfo &Info,
   case Intrinsic::riscv_seg7_load:
   case Intrinsic::riscv_seg8_load:
     return SetRVVLoadStoreInfo(/*PtrOp*/ 0, /*IsStore*/ false,
-                               /*IsUnitStrided*/ false);
+                               /*IsUnitStrided*/ false, /*UsePtrVal*/ true);
   case Intrinsic::riscv_seg2_store:
   case Intrinsic::riscv_seg3_store:
   case Intrinsic::riscv_seg4_store:
@@ -1537,19 +1543,21 @@ bool RISCVTargetLowering::getTgtMemIntrinsic(IntrinsicInfo &Info,
     // Operands are (vec, ..., vec, ptr, vl)
     return SetRVVLoadStoreInfo(/*PtrOp*/ I.arg_size() - 2,
                                /*IsStore*/ true,
-                               /*IsUnitStrided*/ false);
+                               /*IsUnitStrided*/ false, /*UsePtrVal*/ true);
   case Intrinsic::riscv_vle:
   case Intrinsic::riscv_vle_mask:
   case Intrinsic::riscv_vleff:
   case Intrinsic::riscv_vleff_mask:
     return SetRVVLoadStoreInfo(/*PtrOp*/ 1,
                                /*IsStore*/ false,
-                               /*IsUnitStrided*/ true);
+                               /*IsUnitStrided*/ true,
+                               /*UsePtrVal*/ true);
   case Intrinsic::riscv_vse:
   case Intrinsic::riscv_vse_mask:
     return SetRVVLoadStoreInfo(/*PtrOp*/ 1,
                                /*IsStore*/ true,
-                               /*IsUnitStrided*/ true);
+                               /*IsUnitStrided*/ true,
+                               /*UsePtrVal*/ true);
   case Intrinsic::riscv_vlse:
   case Intrinsic::riscv_vlse_mask:
   case Intrinsic::riscv_vloxei:
@@ -1584,7 +1592,7 @@ bool RISCVTargetLowering::getTgtMemIntrinsic(IntrinsicInfo &Info,
   case Intrinsic::riscv_vlseg8ff:
     return SetRVVLoadStoreInfo(/*PtrOp*/ I.arg_size() - 2,
                                /*IsStore*/ false,
-                               /*IsUnitStrided*/ false);
+                               /*IsUnitStrided*/ false, /*UsePtrVal*/ true);
   case Intrinsic::riscv_vlseg2_mask:
   case Intrinsic::riscv_vlseg3_mask:
   case Intrinsic::riscv_vlseg4_mask:
@@ -1601,7 +1609,7 @@ bool RISCVTargetLowering::getTgtMemIntrinsic(IntrinsicInfo &Info,
   case Intrinsic::riscv_vlseg8ff_mask:
     return SetRVVLoadStoreInfo(/*PtrOp*/ I.arg_size() - 4,
                                /*IsStore*/ false,
-                               /*IsUnitStrided*/ false);
+                               /*IsUnitStrided*/ false, /*UsePtrVal*/ true);
   case Intrinsic::riscv_vlsseg2:
   case Intrinsic::riscv_vlsseg3:
   case Intrinsic::riscv_vlsseg4: